Bales are often prepared under conditions of substantial pressure so that the finished product is considerably more dense than the loose material from which it is made.
While it may generally be stated that increased density in such bales is a highly desirable objective, obtaining that goal has in many respects been thwarted because of the limitations of conventional wire and twine tying mechanisms. Beyond a certain level of tension in the wire or twine strands, the mechanisms experience difficulty in holding on to the strands and manipulating the same through the various motions involved in tying the opposite ends of the strands into a satisfactory knot or other type of connection. Moreover, the strands themselves can only withstand certain levels of tension before they will break.
In balers that make a single knot in each loop of twine encircling a bale, one area in which substantial tension is created in the strands stems from the procedure of pulling the strands between the tightly abutting ends of a previous bale and the one being formed in order to progressively lengthen the material in the loop until the forming bale reaches its predetermined size, at which point the opposite ends of the loop are simply tied together and the bale is thereby securely bound. The need to pull the strands between the abutting bales in this manner arises because each strand has one end thereof retained by the tying mechanism while the rest of the strand is draped across the bale chamber. As the growing bale is pushed through the chamber, it presses against the strand draped across the chamber and, because one end is anchored at the tier, the strand must be pulled between the bales by the tier in order to increase the length of the strand along that side of the bale adjacent the tier. While the tension may be relatively low in the strand along its length between the source of supply and the bales, the tension will necessarily be quite higher along that length from the bales to the tier. It is along this latter length that troubles arise.
To overcome this problem, baling machines have been proposed in which each loop comprises two knots. Two runs of twine drawn from two separate supply rolls are knotted at the commencement of formation of a bale. As the size of the bale increases, more twine is drawn from the supply rolls but neither run of twine needs to slide over the surface of the bale and the formed knot remains in the same place on the bale as it increases in size. At the end of a bale forming cycle, two knots are formed in the two twines, the first to tie the completed bale and the next to commence the next bale.
A baler employing such a knotting system is disclosed in U.S. Pat. No. 4,142,746 the drawings and description of which are reproduced below as background to the present invention, which is concerned with an improvement in one of the components of the knotter used in the baler of that patent.
As will become apparent from the detailed description of U.S. Pat. No. 4,142,746 which follows, the knotter comprises a twine holder which tightly grips the two runs of twine to be knotted for the entire duration of the process of tying the two desired knots. A device known as a bill hook rotates in front of the twine holder to form the knots and a cutter separates each knot as it is formed from the twine runs gripped by the holder. A twine finger arranged below the bill hook is pivoted to bring the runs of twine within the reach of the bill hook at the commencement of formation of each of the two knots.
During the formation of the first of the two knots, that is to say the knot used to complete a loop wrapped around a bale, the twine is kept in tension by the compressed bale and this results in a tight knot with long tails projecting from the knot. Such a knot has no tendency to come undone during handling of the bale. During the formation of the second knot, on the other hand, the runs of twine still gripped by the holder are only under the tension of the runs of twine drawn from the supply rolls. These runs may have a spring arm for taking up slack and a friction device to resist unraveling of the rolls but the tension cannot be set too high on account of the noise and wear that the high tension would cause during the formation of the bales. As a consequence, the second knot is currently not as tight as the first and has shorter tails protruding from it. Because of this, the second knot, i.e. the knot tying the twine runs to each other prior to formation of a new bale, risks become unfastened while the bales are being handled.